Pump



E. H. DODGE PUMP Filed June 29, 1953 R m E e M m o 4 H m @N .1. mm N mm a @N H E w I'Pl om om NM N w Y N B S NN NH 5 VIII. x r1' mm l 1mm .w I filwm wm m i A ii! an m MN on E m mm 7/92 mm om mm a Q 5 1 3 w 2 i m 2 P 0% v @H ATTORNEYS Patented Sept. 28, 1954 PUMP Elwin H. 'Dodge, W atertown, N. Y., assignor to The New York Air Brake Company, a corporation of New Jersey Application June 29, 1953, Serial No. 364,604

'5Claims. 1

This invention relates to reciprocating piston pumps. Specifically, it relates to improved means whereby the pistons in a swash plate pump are maintained in engagement with the surface of the swash plate at all times during operation of the pump.

The recent demands for increased pressure and rotary speeds in pumps of this type have resulted in a necessity for improved means for moving the pistons during the suction stroke. It had been common practice to use springs to accomplish this purpose. Various mechanical means have been proposed and have proved successful, but they add considerably to the weight of the pump which is undesirable in aircraft installations. The present invention relates to simple fluid pressure operated means for returning the pistons and may be used whether or not the pump is operated with a positive inlet pressure. Furthermore it does not require the use of an auxiliary pump to create the pressure to return the pistons.

The pump embodying the present invention comprises two circular series of reciprocating pistons, each series having its own swash plate. The two swash plates are carried by a single driven shaft and are arranged with their thrust surfaces facing and parallel with each other. Each of the cylinder bores in one of the two series is alined with a cylinder bore in the other series. The pistons, reciprocable in these bores, are provided with an axial counterbore'extending inward from their head end. A single tubular member mounted in the counterbores extends between the alined pistons of each series. Liquid at pump discharge pressure is admitted to the interior of this tubular member and serves during operation of the pump to apply liquid at discharge pressure over a minor portion of the area of each piston at all times whereby the pistons are continuously biased into thrust engagement with the swash plates. The length of the tubular member is such that there is some clearance between it and the bottoms of the counterbores in which it is carried. This clearance may be varied but the tubular member must be of such a length that after the pump stands idle and the pistons are no longer positively biased against the swash plate due to dissipation of pressure in the pump discharge they can not assume a position in which they are not engaged by the thrust plate during at least a portion of its rotation.

The preferred embodiment of the invention will be described having reference to the accompanying drawing which is an axial section of a pump embodying the preferred form of the in-. vention.

As shown in the drawing, the pump comprises a three-part housing, i. e., inlet sections 5 and 6 and a discharge section 7, therebetween. These sections are held in assembled relation by means of suitable bolts '8, two of which are shown in the drawing.

The inlet section '6 encloses -a cam chamber 9 into which the inlet connection I! extends. The inlet section 5 encloses a cam chamber I 2 into which the inlet connection it extends. Leakage between mating surfaces of sections -5,' 6 and l is prevented by suitable sealing means I4. A cylinder block l5'is mounted between a shoulder 16 in the inlet section 5 and a shoulder I? in the discharge section 1. A groove I8 is provided in the outer periphery of the inner end of the cylinder block l5 and an O-ring i9 is mounted therein to prevent leakage between the discharge section '1 and block 15. Cylinder block 1'5 is provided-with a circular series of cylinder bores 21. Each of the bores 21 is provided with an annular inlet groove 22. A drilled port 23 extends between each of the grooves 22 and the cam chamber [2. An identical cylinder block 2d is similarly mounted between the discharge section .1 and the inlet section 5. The construction and mounting .of this cylinder block will be apparent from the construction .and mounting of the cylinder block l5 and it need not therefore be described. Each of the cylinder bores 21 in the cylinder block i5 is alined with a corresponding cylinder bore 2| in the cyl-' inder block 24.

Each of the blocks I5 and 2A is provided with a central aperture and a main shaft 25 extends therethroug'h. The outer end of the shaft 25 is adapted for connection to any suitable driving means. Mounted on the shaft 25 within the cam chambers I2 and 9 respectively are two swash plates 26 and 21. The thrust surfaces of these swash plates are parallel with and face one another. The shaft .25 and the swash plates 26 and 21 mounted thereon are carried by suitable ball bearings 28 as shown in the drawing. The outer end of the shaft 25 is provided with a conventional .oil seal assembly generally indicated by the reference numeral 29.

,Reciprocable in each of the cylinder bores 2| is a piston 13!] which carries at its outer end a universally tiltable thrust shoe 3|. Shoes 3! are arranged to engage thethrust surface of the corresponding swash plate 2t or 27. Each of the pistons an is provided with an axial counterbore which extends inward from its inner end. Radial ports 32 extend from the inner end of the counterbore to the outer periphery of the pistons 33. A tubular member 33 is mounted. in the counterbores of each pair of alined pistons. This tubular member 33 is provided with a port 34 which aifords communication between the interior of the tubular member 33 and the discharge chamber 35 which is defined in the discharge section I between the cylinder blocks and 24. Discharge connection 45 extends outward from the discharge chamber 35 through the section I.

A sleeve 35 encircles the shaft 25 between the two cylinder blocks. This sleeve is provided at its ends with flanges 31 which project into annular recesses 38 provided in the cylinder blocks l5 and 24. Adjacent to the annular recesses 38, an annular groove 39 is formed in each of the cylinder blocks. An O-ring4l is mounted therein and reacts against the sleeve 36 when the pump is assembled. This assembly serves to seal against the leakage of fluid along the shaft 25 from the discharge chamber 35. Two disc-like discharge valves 42 encircle and are closely fitted to each of the tubular members 33. A compression spring 43 reacts between each pair of discharge valves 42 and biases them toward the cylinder blocks l5 and 24.

Fluid admitted to the cam chambers 9 and I2 serves to lubricate the thrust surfaces of the swash plate and the bearings 28. Fluid from the cam chambers is admitted to the working spaces above the pistons through the passage 23 and the grooves 22. As the piston overtravels the annular groove 22 the fluid which is trapped in the working space is forced outward past the discharge valve 42 into the discharge chamber 35. It will be seenfrom the drawing that the alined pistons in each series are arranged so that their suction and discharge strokes are out of phase. During the suction stroke, the piston shoes 3! are maintained in engagement with the thrust surface of the swash plates 26 and 21 by means of fluid at discharge pressure which reacts over a minor portion of the area of the piston (the area of the counterbores). In this way it is possible to do away with the customary return springs and other mechanical piston return means.

The overall length of the two alined pistons and the tubular member associated therewith is not greater than the axial distance between the thrust faces of the two swash plates but is greater than the axial separation of the thrust surfaces minus the effective piston stroke. By effective stroke is meant the stroke between closure of the inlet port and the uppermost position of the piston. It will be seen that this minimum length is such that if pressure from the discharge chamber 35 has been dissipated when the pump is idle and if the pistons have moved to the upper limits of their motion each will be engaged during a part of each complete rotation of the swash plate. This assures that the pump will always resume operation after standing idle regardless of the position to which the pistons have moved.

In the preferred embodiment the combined length of the pistons and the tubular member 33 is only slightly less than the axial spacing between the two swash plates. This is the preferred arrangement because it enables a smoother starting operation than would be the case if the minimum length defined above were used.

The radial ports 32 admit fluid between the piston and the cylinder bores for lubrication. Although in the preferred form of the invention the tubular members 33 pass through the discharge valves, it will be apparent to those skilled in the art that this is not the only possible arrangement of these parts. In order to avail of the teachings of the invention, it is only necessary that the tubular member extend between two pistons which operate out of phase with each other and that it be provided with means for receiving liquid at discharge pressure in its interior whereby at least a portion of the cross sectional area of the piston is subject to discharge pressure during the suction stroke to urge the piston into engaging relationship with the thrust surfaces of the associated swash plates.

What is claimed is:

1. A pump comprising a housing; two cylinder blocks mounted therein, a discharge chamber defined thereby; each cylinder block. having a circumferential series of cylinder bores therein, the bores of one series being alined with the bores in the other series and each one having an inlet connection; a spring biased discharge valve controlling fiow from said bores to said discharge chamber; a piston reciprocable in each of said bores; a drive shaft mounted in said housing and extending through said cylinder blocks and the discharge chamber; means a'lfording inclined, opposed, parallel thrust surfaces mounted on the shaft, the pistons arranged to engage said surfaces; axial counterbores in the proximate ends of the pistons of each series; and a tubular member mounted in the alined counterbores of each series of pistons, each of the tubular members having a port through which fluid from the discharge chamber is admitted into the bore thereof.

2. The combination defined in claim 1; the overall length of each thrust member and the alined pistons in which it is mounted is less than the axial spacing between the thrust surface minus the effective piston stroke.

3. The combination defined in claim 1 in which said discharge valves each comprise an annular member encircling said tubular members and a spring reacting between the annuli encircling each tubular member.

4. The combination defined in claim 1; each of said pistons having at least one through port extending outward from the counterbore therein.

5. A pump comprising a housing; means defining two circular series of cylinder bores therein; means affording an inlet connection to each of said bores; a discharge chamber defined by said housing and said first named means; a discharge valve associated with each of said bores; a piston reciprocable in each of said bores; two identical cams driven at equal speeds and each engaging one of the series of pistons, the pistons each having a counterbore therein; a thrust member slidably mounted in said counterbores and extending between the pistons of each series which are 180 out of phase with each other, said thrust members having a passage extending end to end therethrough and having a port therein through which fluid at discharge pressure may be admitted to said passage.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,e31,686 Deschamps Dec. 2, 1947 2,492,688 Dall Dec. 27, 1949 2,565,582 White Aug. 28, 1951 FOREIGN PATENTS Number Country Date 553,483 Great Britain May 24, 1943 

